Vehicle overheight detector device and method

Abstract

A dual-beam photoelectric switch and method adapted for detecting overheight vehicles that emits and detects red light along an optical axis, and emits and detects infrared light along a parallel and oppositely oriented optical axis. A fault detector receives signals from the light detectors, processes the signals in accordance with a predetermined logic and produces a pair of outputs indicating the fault status of the light detectors. An alarm mode component receives the signals of light detectors and the fault status outputs, enables and disables recognition of signals of the light detectors in relation to the fault status outputs, and triggers certain outputs in accordance with a predetermined logic.

What is claimed is: 
     
       1. A dual-beam type photoelectric switching device comprising: a. a first transmitter for emitting red light in a first direction along a first optical axis, and a first detector placed along the first optical axis, said first detector for receiving red light emitted from the first transmitter and said first detector for outputting a signal indicating the presence and absence of red light emitted from the first transmitter;   b. a second transmitter for emitting infrared light in a second direction along a second optical axis, and a second detector placed along the second optical axis, said second detector for receiving infrared light emitted from the second transmitter and said second detector for outputting a signal indicating the presence and absence of infrared light emitted from the second transmitter; wherein the first optical axis and the second optical axis are approximately parallel to each other and wherein the first direction and the second direction are approximately opposite of each other;   c. a fault detector for receiving the signal from the first light detector and the signal from second light detector, processing said signals and producing outputs indicating fault status of said light detectors; and   d. an alarm mode component for receiving the signal of the first detector, the signal of the second detector and the fault status outputs, and for triggering certain outputs in accordance with a predetermined logic.   
     
     
       2. The device of claim 1 wherein the fault detector includes: a. a first accumulator for measuring a first elapsed time following interruption of normal reception of red light by the first light detector until reestablishment of normal reception of red light by the first light detector;   b. a first comparator for comparing the first elapsed time with a first predetermined value and for outputting a first fault signal related to the first elapsed time exceeding the first predetermined value;   c. a second accumulator for measuring a second elapsed time following interruption of normal reception of infrared light by the second light detector until reestablishment of normal reception of infrared light by the second light detector; and   d. a second comparator for comparing the second elapsed time with a second predetermined value and for outputting a second fault signal related to the second elapsed time exceeding the second predetermined value.   
     
     
       3. The device of claim 1 wherein the alarm mode component further comprises: a. a circuit for: i. outputting an alarm signal in relation to the alarm mode component receiving the fault status outputs, and   ii. enabling and disabling recognition of the signals of the detectors in relation to the fault status outputs; and     b. a circuit for comparing the signal of the first detector and the signal of the second detector in accordance with a predetermined logic and outputting a signal.   
     
     
       4. The device of claim 2, wherein: a. the fault detector further comprises a component for delaying termination of the first fault signal and a component for delaying termination of the second fault signal, for noise reduction;   b. the first accumulator of the fault detector further comprises a component for delaying initiation of measuring of elapsed time and a component for delaying termination of measuring elapsed time, for noise reduction; and   c. the second accumulator of the fault detector further comprises a component for delaying initiation of measuring of elapsed time and a component for delaying termination of measuring elapsed time, for noise reduction.   
     
     
       5. The device of claim 4, wherein the component for delaying termination of the first fault signal of the fault detector is a timer and the component for delaying termination of the second fault signal of the fault detector is a timer. 
     
     
       6. The device of claim 4 wherein the component for delaying initiation of measuring of elapsed time of the first accumulator of the fault detector is a first integrating capacitor and the component for delaying termination of measuring elapsed time of the first accumulator of the fault detector is the first integrating capacitor, and the component for delaying initiation of measuring of elapsed time of the second accumulator of the fault detector is a second integrating capacitor and the component for delaying termination of measuring elapsed time of the second accumulator of the fault detector is the second integrating capacitor. 
     
     
       7. The device of claim 6 wherein the first integrating capacitor has a discharge rate twice that of its charge rate, and wherein the second integrating capacitor has a discharge rate twice that of its charge rate. 
     
     
       8. The device of claim 1 for detecting overheight vehicles traveling along a roadway, wherein the first optical axis and the second optical axis define a plane, and the plane and the roadway are substantially parallel to each other, with the shortest distance between the plane and the roadway being substantially equivalent to the maximum vehicle height desired to be measured. 
     
     
       9. A dual-beam type photoelectric switching device for detecting overheight vehicles traveling along a roadway, comprising: a. a first transmitter for emitting red light in a first direction along a first optical axis, and a first detector placed along the first optical axis, said first detector for receiving red light emitted from the first transmitter and said first detector for outputting a signal indicating the presence and absence of red light emitted from the first transmitter;   b. a second transmitter for emitting infrared light in a second direction along a second optical axis, and a second detector placed along the second optical axis, said second detector for receiving infrared light emitted from the second transmitter and said second detector for outputting a signal indicating the presence and absence of infrared light emitted from the second transmitter; wherein the first optical axis and the second optical axis are approximately parallel to each other and wherein the first direction and the second direction are approximately opposite of each other; wherein the first optical axis and the second optical axis define a plane, and the plane and the roadway are substantially parallel to each other, with the shortest distance between the plane and the roadway being substantially equivalent to the maximum vehicle height desired to be measured;   c. a fault detector for receiving the signal from the first light detector and the signal from second light detector, processing said signals and producing outputs indicating fault status of said light detectors, said fault detector having: i. a first accumulator for measuring a first elapsed time following interruption of normal reception of red light by the first light detector until reestablishment of normal reception of red light by the first light detector, said first accumulator having a first integrating capacitor for delaying the initiation of measuring elapsed time and for delaying the termination of measuring elapsed time,   ii. a first comparator for comparing the first elapsed time with a first predetermined value and for outputting a first fault signal related to the first elapsed time exceeding the first predetermined value,   iii. a first timer for delaying termination of first fault signal,   iv. a second accumulator for measuring a second elapsed time following interruption of the normal reception of infrared light by the second light detector until reestablishment of normal reception of infrared light by the second light detector, said second accumulator having a second integrating capacitor for delaying the initiation of measuring elapsed time and for delaying the termination of measuring elapsed time,   v. a second comparator for comparing the second elapsed time with a second predetermined value and for outputting a second fault signal related to the second elapsed time exceeding the second predetermined value, and   vi. a second timer for delaying termination of second fault signal; and     d. an alarm mode component for receiving the signal of the first detector, the signal of the second detector and the fault status outputs, and for triggering certain outputs in accordance with a predetermined logic, said alarm mode component having: i. a circuit for: (a) outputting an alarm signal in relation to the alarm mode component receiving the fault status outputs, and   (b) enabling and disabling recognition of the signals of the detectors in relation to the fault status outputs,     ii. a circuit for comparing the signal of the first detector and the signal of the second detector in accordance with a predetermined logic and outputting a signal.     
     
     
       10. A method for detecting an object using a dual-beam type photoelectric switching device comprising the steps of: a. emitting red light from a first transmitter in a first direction along a first optical axis, receiving red light emitted from the first transmitter by a first detector placed along the first optical axis, and outputting a signal with the first detector to indicate the presence and absence of red light emitted from the first transmitter;   b. emitting infrared light from a second transmitter in a second direction along a second optical axis, receiving infrared light emitted from the second transmitter by a second detector placed along the second optical axis, and outputting a signal with the second detector to indicate the presence and absence of infrared light emitted from the second transmitter; wherein the first optical axis and the second optical axis are approximately parallel to each other and wherein the first direction and the second direction are approximately opposite of each other;   c. receiving the signal from the first light detector and the signal from second light detector with a fault detector, processing said signals and producing outputs indicating fault status of said light detectors; and   d. receiving the signal of the first detector, the signal of the second detector and the fault status outputs, and triggering certain outputs in accordance with a predetermined logic.   
     
     
       11. A method for detecting overheight vehicles traveling along a roadway using a dual-beam type photoelectric switching device comprising the steps of: a. emitting red light from a first transmitter in a first direction along a first optical axis, receiving red light emitted from the first transmitter by a first detector placed along the first optical axis, and outputting a signal with the first detector to indicate the presence and absence of red light emitted from the first transmitter;   b. emitting infrared light from a second transmitter in a second direction along a second optical axis, receiving infrared light emitted from the second transmitter by a second detector placed along the second optical axis, and outputting a signal with the second detector to indicate the presence and absence of infrared light emitted from the second transmitter; wherein the first optical axis and the second optical axis are approximately parallel to each other and wherein the first direction and the second direction are approximately opposite of each other;   c. receiving the signal from the first light detector and the signal from second light detector with a fault detector, processing said signals and producing outputs indicating fault status of said light detectors; said receiving step further comprising the following steps: i. measuring by use of a first accumulator a first elapsed time following interruption of normal reception of red light by the first light detector until reestablishment of normal reception of red light by the first light detector, said first accumulator having a first integrating capacitor for delaying the initiation of measuring elapsed time and for delaying the termination of measuring elapsed time,   ii. comparing the first elapsed time with a first predetermined value and outputting a first fault signal related to the first elapsed time exceeding the first predetermined value,   iii. delaying termination of first fault signal for noise reduction,   iv. measuring by use of a second accumulator a second elapsed time following interruption of normal reception of infrared light by the second light detector until reestablishment of normal reception of infrared light by the second light detector, said second accumulator having a second integrating capacitor for delaying the initiation of measuring elapsed time and for delaying the termination of measuring elapsed time,   v. comparing the second elapsed time with a second predetermined value and outputting a second fault signal related to the second elapsed time exceeding the second predetermined value, and   vi. delaying termination of second fault signal for noise reduction; and     d. receiving the signal of the first detector, the signal of the second detector and the fault status outputs, with an alarm mode component and triggering certain outputs in accordance with a predetermined logic, the receiving and triggering step having the steps of: i. outputting an alarm signal in accordance with a predetermined logic related to the alarm mode component receiving the fault status outputs,   ii. enabling and disabling recognition of the signals of the detectors in relation to the fault status outputs, and   iii. comparing the signal of the first detector and the signal of the second detector in accordance with a predetermined logic and outputting a signal.